Digital Subscriber Line (DSL) is a technology that is used to convey high-bandwidth consuming data, such as Internet to subscribers, over ordinary twisted pair copper wire telephone lines. Due to the increasing number of services and applications which require transmission of data along DSL communication lines, there is an ever-growing demand to increase the bandwidth for transmissions and the transmission rates. The signal-to-noise ratio (SNR) of the communication lines has a strong adverse effect upon the performance of a broadband network. Crosstalk is considered to be a major source of noise in DSL systems, thereby affecting the SNR experienced along the communication link.
Crosstalk is a phenomenon by which one twisted pair generates electromagnetic interference onto another twisted pair, normally when the two pairs run in proximity to each other. When a signal passes through one twisted pair it may be adversely influenced by the crosstalk originated in another twisted pair. Accordingly the signal may be misinterpreted at the receiving side, which in turn would lead to errors in the digital bit stream. It is possible that some twisted pairs interfere with a number of twisted pairs but do not interfere with other twisted pairs belonging to the same cable. A typical DSL cable contains several binders grouped together to form a cable, where a binder is used to bundle multiple insulated copper pairs together in the communication network.
Even though the copper wires in each binder are manufactured in a way that reduces crosstalk, Far End Crosstalk (FEXT) may still occur. FEXT is the result of signals transmitted at one end of the cable, and being coupled at the far end of the cable. In VDSL2 technology, mainly used in broadband DSL networks, FEXT is the main source of crosstalk due to the Frequency Division Duplexing (FDD) used to combine downstream and upstream transmissions at a single twisted pair. Dynamic Spectrum Management (DSM) is used among other things to reduce interferences within a DSL network. The crosstalk problem is particularly felt in lines that are close to each other in a binder, for example in a binder of 25 lines within a 100 lines cable.
Several solutions and DSM methods which are known in the art deal with the adverse effect of the crosstalk. For example, US published application No. 2011222611 discloses a method for managing transmission resources in a DSL system for minimizing cross-talk interference in a cable or cable binder of the access network comprising N lines. The method describes determining a set of relevant lines comprising lines that create interference for a particular line, and applying, for that particular line, an algorithm for resource management using the determined relevant lines' set. However since the method disclosed in this publication considers one particular line at a time, it does not address the problem which the present invention seeks to address, namely, how to identify groups of lines having mutually strong interference. It could be for example that line No. 1 is mainly affected by line No. 2 and line No. 3, whereas line No. 2 is mainly affected by line No. 4 and line No. 5. Yet, this information cannot be used in accordance with the teaching of US 2011222611 to partition the lines into groups. Hence the solution described by this publication does not enable further reduction of the computational resources for carrying out DSM algorithms, nor can it be used to assist the network operator in providing and managing the DSL service.
The known methods fail to provide an adequate and comprehensive enough solution to the crosstalk problem, and the present invention seeks to provide a solution that overcomes the limitations of the prior art methods.